The theory of Deep Crustal Heating predicts a rock-bottom
luminosity for transiently accreting neutron stars in
quiescence (qNSs), set by by the temperature of the NS core
which is heated by crustal reactions during outbursts.
Chandra observations of two such objects -- Cen X-4 and Aql
X-1 -- confirm previous work that qNSs emit such a
luminosity. The H atmosphere spectra imply an emission area
radius consistent with that of a neutron star; however,
large systematic uncertainties in the NS distance (D)
produce a large systematic uncertainty in the NS radius (r)
since what is measured is the angular size (r/D). Future
work will be directed toward discovery and spectroscopy of
qNSs in globular clusters, whose distances are relatively
precisely known. I will present observational results from
the Chandra Summer 2000 observation of Cen X-4 and the
Spring 2001 observation of Aql X-1. This work is funded by
the NASA/Chandra Guest Observer Program.